Plunge milling is commonly viewed as an extremely efficient method for removing large amounts of material (e.g., 20% to 60% or more than traditional peripheral milling methods) from a workpiece blank. In such a milling process, a cutting tool is plunged axially and repeatedly into the workpiece blank in a series of overlapping passes to create an intermediate workpiece. The intermediate workpiece is then de-roughed and finished to create the final workpiece. Plunge milling is distinct from the more traditional peripheral milling methods where a cutting tool with one or more side cutting elements is moved transversely with respect to its rotational axis such that cutting occurs at the periphery of the rotating cutting tool rather than at the axial end of the cutting tool in the case of plunge milling.
An axial cutting tool typically comprises a spindle and a holder which carries cutting elements. The cutting elements are almost always replaceable inserts as they are the high-wear items in a plunge milling system. In any event, a plunge cutting tool can have as few as one cutting element, but usually has a plurality of cutting elements arranged around the circumference of the holder. The cutting elements are designed and arranged on the holder so that their axial edges form the cutting surfaces. Thus, for example, in a vertical plunge milling arrangement, the bottom edge of the cutting element defines its cutting surface.
The spindle of the axial cutting tool is attached to a feed mechanism for controlled rotational and axial movement of the axial cutting tool. During a plunge milling operation, a radially outer edge portion of the rotating axial cutting tool is aligned with a to-be-removed region of the workpiece blank and moved axially so that the cutting elements engage the material. The rotation of the cutting elements removes the material in crescent-shaped cuts and the axial movement continues until the tool reaches a predetermined stop-pass position. Accordingly, material is removed from the workpiece blank in a straight axial path.
Upon reaching the stop-pass position, the tool is axially retracted and then shifted laterally for alignment with an adjacent to-be-roughed (and usually overlapping) region of the workpiece blank for another pass of the cutting tool. These passes can be continued along the length of the workpiece. To prevent any interference between the cutting inserts and the workpiece blank during the retracting movement, the tool can be shifted laterally outward just prior to retraction.
A hallmark characteristic of plunge milling has conventionally been that the axial cutting tool moves only in the axial direction while in engagement with the material. This concentration on axial tool movement during cutting, and the avoidance of transaxial movement, has traditionally been viewed as important to increasing material removal rates and prolonging tool life.